S. Galović

Theory of photoacoustic effect in media with thermal memory

This paper presents a model for indirect photoacoustic response that includes thermal memory effects. At low frequencies, the model reduces to the well-known thermal piston model of photoacoustic response given by Rosencweig and Gersho. However, at high frequencies, the presented model predicts resonant behavior of amplitudes and phases of photoacoustic response and determines the respective resonant frequencies. The results of the presented model enable experimental determination of standard thermal properties of solids (thermal diffusivity and thermal conductivity), as well as thermal memory properties, thermal relaxation time, and heat propagation speed.

The vibron dressing in α-helicoidal macromolecular chains

We present a study of the physical properties of the vibrational excitation in α-helicoidal macromolecular chains, caused by the interaction with acoustical and optical phonon modes. The influence of the temperature and the basic system parameters on the vibron dressing have been analyzed by employing the simple mean-field approach based on the variational extension of the Lang—Firsov unitary transformation. The applied approach predicts a region in system parameter space where one has an abrupt transition from a partially dressed (light and mobile) to a fully dressed (immobile) vibron state. We found that the boundary of this region depends on system temperature and the type of bond among structural elements in the macromolecular chain.

Photoacoustic signal and noise analysis for Si thin plate: Signal correction in frequency domain

Methods for photoacoustic signal measurement, rectification, and analysis for 85 μm thin Si samples in the 20-20 000 Hz modulation frequency range are presented. Methods for frequency-dependent amplitude and phase signal rectification in the presence of coherent and incoherent noise as well as distortion due to microphone characteristics are presented. Signal correction is accomplished using inverse system response functions deduced by comparing real to ideal signals for a sample with well-known bulk parameters and dimensions. The system response is a piece-wise construction, each component being due to a particular effect of the measurement system. Heat transfer and elastic effects are modeled using standard Rosencweig-Gersho and elastic-bending theories. Thermal diffusion, thermoelastic, and plasmaelastic signal components are calculated and compared to measurements. The differences between theory and experiment are used to detect and correct signal distortion and to determine detector and sound-card characteristics. Corrected signal analysis is found to faithfully reflect known sample parameters.

Thermal memory influence on the thermoconducting component of indirect photoacoustic response

In this paper, a model of the thermoconducting component of the indirect photoacoustic (PA) response is derived that includes thermal memory properties of the examined material and its fluid environment. A comparison is made between the derived model and the classic one, which neglects the influence of thermal memory. It has been shown that, at modulation frequencies lower than a certain boundary frequency of the light source, these models tend to overlap, while at higher frequencies, noticeable differences occur. The boundary frequency depends on heat propagation velocity through the sample and its thickness. This observation limits the validity domain of previous models to a range lower than the boundary frequency, offering, at the same time, the possibility of obtaining thermal memory properties using PA effects at frequencies above it.

On the applicability of the effective medium approximation to the photoacoustic response of multilayered structures

If the model of the photoacoustic (PA) response of an investigated system contains many unknown parameters, as is the case with multilayered samples, then the inverse procedure for the calculation of the parameters is highly sensitive to experimental noise. The problem cannot be solved by developing the experimental setup or by data acquisition methods, but only by an improvement of the theoretical approach. This paper presents an analysis of the applicability of the effective medium approximation to the PA response of multilayered samples. It has been shown that the theory is not applicable to the general case, and explicit expressions for the effective values of thermal diffusivity and heat propagation speed have been derived for some special cases.

On the vibron nature in the system of two parallel macromolecular chains: The influence of interchain coupling

Abstract We studied the properties of the intramolecular vibrational excitation (vibron) at finite temperature in a system which consists of two parallel macromolecular chains. It was assumed that vibron interacts exclusively with dispersionless optical phonons and the whole system is considered to be in thermal equilibrium. Particular attention has been paid to the examination of the impact of the temperature and strength of the interchain coupling on the small polaron crossover. For that purpose we employed partial dressing method which enables the study of the degree of the phonon dressing of the vibron excitations in a wide area of system parameter space. We found that in the non-adiabatic regime the degree of dressing as a function of coupling constant continuously increases reflecting the smooth transition of the slightly dressed, practically free vibron, to a heavily dressed one: small polaron. As “adiabaticity” rises this transition becomes increasingly steeper, and finally, in the adiabatic limit, a discontinuous “jump” of the degree of dressing is observed. The interchain coupling manifests itself through the increase of the effective adiabatic parameter of the system.

On the vibron-polaron damping in quasi 1D macromolecular chains

The properties of the intramolecular vibrational excitation (vibron) in a quasi 1D macromolecular structure are studied. It is supposed that due to the vibron interaction with optical phonon modes, a vibron might form partially dressed small polaron states. The properties of these states are investigated in dependence on the basic system parameters and temperature of a thermal bath. We also investigate the process of damping of the polaron amplitude as a function of temperature and vibron-phonon coupling strength. Two different regimes of the polaron damping are found and discussed.

The influence of interchain coupling on intramolecular oscillation mobility in coupled macromolecular chains: The case of coplanar parallel chains

We enlarge our results from the study of the hopping mechanism of the oscillation excitation transport in 1D model of one biologica-likel macromolecular chain to the case of a system composed from two 1D parallel macromolecular chains with consideration of the properties of intramolecular oscillation excitations. We suppose, that due to the exciton interaction with thermal oscillation (generated by mechanical phonon subsystem) of structural elements (consisting of the peptide group) of the chains, the exciton becomes by self trapped and forms the polaron state. We suggest a model which generalizes the modified Holstein polaron model to the case of two macromolecular chains and find that because of the interchain coupling, the exciton energy band is splitted into two subbands. The hopping process of exciton migration along the macromolecular chains is studied in dependence of system parameters and temperature. We pay an special attention to the temperature range (near T = 300 K) in which living cells opera...

Vibron Self-trapped States in Biological Macromolecules: Comparison of Different Theoretical Approaches

We present a study of the applicability of the variational treatments based on using of the modified Lang-Firsov unitary transformation (MLF method) in the investigation of the vibron self-trapped states in biological macromolecular chains. Here we compare the values of the ground state energy predicted by MLF methods with the values of the ground state energy predicted by the standard small-polaron theory, for various values of the basic energy parameters of the system. We obtain regions in system parameter space where MLF approach gives better description of the vibron states.

Photothermal characterization of polymer-based three-layer nanoelectronic structures

The generalized model of surface temperature variations of a three-layer structure irradiated by intensity modulated laser beam was derived, including thermal memory effects. In the specific case of a polymer layer sandwiched between two thin metal foils the model was simplified by electrical analogy. It allowed formulation of unambiguous inverse procedure for estimation of dominating system thermal properties of system from measured photothermal spectra.